1. Field of the Invention
The present invention relates to a fire monitoring system.
2. Description of the Prior Art
A so-called general fire detector and a so-called analog detector are conventionally known for use in monitoring an area for the presence of fire. In a general fire detector, a signal/power supply zone line is short-circuited with low impedance during operation. An analog detector has an address for each sensor and supplies an analog signal corresponding to a quantity such as temperature or smoke concentration to a receiver by address sampling by the receiver. In a fire alarm system disclosed in Japanese Patent Disclosure (Kokai) No. 59-202595, the above fire detectors are used in a single fire receiver at the same time.
The system using an analog detector has many advantages over a system using general ON/OFF type detectors. Such a system can identify an operating detector and can determine a fire by detecting a variation over time of an analog signal of a given analog detector or by comparing it with an analog signal of an adjacent analog detector. Therefore, the system can perform fire monitoring with higher reliability and fewer lines as compared with a system using ON/OFF fire detectors.
As described above, highly reliable fire information can be obtained by installing a fire alarm system using analog detectors to the entire building or the like. However, an operation circuit using a microprocessor such as a CPU and a digital transmitter having relatively large capacities and high transmission speeds are required, hence the system becomes complex and expensive. In addition, it is difficult to install such a fire alarm system in a building where a fire alarm equipment using an ON/OFF fire detector has already been installed.